(1) Summary of the Invention
The present invention relates to an improved firestop stack fitting which has a flammable conduit and extension and yet prevents the spread of fire between floors in a building. In particular, the present invention relates to a fitting which uses only a non-flammable plug and a non-flammable sleeve inside the fitting as the essential non-flammable elements which combine together to prevent the spread of fire between floors when the plug is released by the fire.
(2) Prior Art
My U.S. Pat. No. 4,583,546 shows the closest prior art. In this firestop stack fitting the main conduit and extension conduit were made of cast iron or some other non-flammable material. This combination works very well; however, it is expensive to manufacture. It was thought by the inventor that the conduit and extension had to be non-flammable in order to make the fitting operative.